Linear polyesters from p, p&#39;-sulfonyl dibenzoic acid plus aliphatic dibasic branched-chain acids condensed with a glycol



United States LINEAR POLYESTERS FROM p,p'-SULFONYL Di- BENZOIC ACID PLUS ALIPHATIC DIBASIC BRANCHED-CHAlN ACIDS CONDENSED WITH A GLYCOL 23 Claims. .(Cl. 2 0,45

This application relates to valuable linear polyesters prepared by condensing a p,p-sulfonyl dibenzoic acid diester in conjunction with an aliphatic branched-chain dibasic acid diester containing at least 4 carbon atoms with a polymethylene glycol and/or an aliphatic ether glycol.

It is an object of this invention to provide novel interpolyesters as described herein. It is another object to provide a process as described herein for preparing valuable interpolyesters. Other objects will become apparent hereinafter.

This application is a continuation-in-part of my copending application, Serial No. 143,594, filed February 10, 1950, now U. S. Patent No. 2,614,120, dated October 14, 1952. In that application sulfonyl dibenzoic acid is called bis (dicarboxydiphenylsulfone).

Highly polymeric esters of terephthalic acid and various glycols, for example, ethylene glycol, trimethylene glycol, hexmethylene glycol, etc., are well known, and have been used in the preparation of linear, highly polymeric polyesters having properties including that of being capable of being formed into useful filaments, fibers and the like, and having high melting points and a low degree of solubility in organic solvents. Linear polyesters prepared from other aromatic dicarboxylic acids have also been described in the prior art and contemporary art.

interpolyesters of terephthalic acid and other dibasic acids condensed with dihydroxy compounds have also been described.

None of the polyesters known in the prior art are easily prepared without high cost. Moreover, they do not possess the herein-described highly advantageous properties which render them especially suitable for processing by injection molding and extrusion methods. Furthermore, the known polyesters do not possess the low modulus of elasticity resulting in high resiliency and reversible extensibility possessed by the interpolyesters described herein.

It has now been found that p,p-sulfonyl dibenzoic acid or its esters or its acid chloride plus an aliphatic branchedchain dibasic acid or diester thereof can be condensed with a polymethylcne glycol and/ or an aliphatic ether glycol to produce a new kind of linear interpolyester having highly valuable properties which are superior to those of the linear polyesters described in the prior art. Thus, my new interpolyesters can be prepared having a relatively wide softening range and good flow characteristics whereby they are quite valuable for the production of shaped b e t b in ecti mslding or ex n t od- Thes novel interpolyesters can be prepared so as to soften at temperatures which are above about 180 C. Useful interpolyesters can also be prepared which soften at lower temperatures.

The novel interpolyesters described herein are quite useful inthe making of electrical insulation.

These novel interpolyesters can be prepared so as to have especially valuable properties when formed into fibers by melt spinning methods followed by drawing.

Patented May 1, 1956 These. fibers can be prepared so as to have a reversible extensibility of about 30% or more.

The modulus of elasticity of these interpolyesters is unusually low compared to known polyesters; accordingly, these interpolyesters are quite rubbery and resilient. They are highly valuable where a high degree of elastic recovery is desirable, e. g., gaskets, packing, resilient elastic fibers, flexible tubing, elastic clothing, etc. Although interpolyesters can be prepared which soften at 200 C. or higher, many valuable products can be produced which soften at lower tempratures.

My novel interpolyesters may contain as constituents thereof small percentages of the man and/or the m,p isomers of the p,p-sul fonyl dibenzoic compound without significant deleterious efiect on the properties of these interpolyesters. In fact, when the interpolyester is to be employed for purposes other than for making fibers, substantial quantities of these isomers can be employed with some advantageous results, especially as regards increasing the softening temperature range.

Two of the outstanding qualities of the interpolyesters of this invention are their excellent dimensional stability and low degree of water absorptivity. This results in superior resistance to dimensional change despite changes in atmospheric humidity or immersion in aqueous solutions.

The interpolyesters of this invention have melting points which are up to as much as or more than 50C. higher than corresponding interpolyesters prepared from dibasic acidic compound combinations described in the prior art. This characteristic results in a much greater effective range of utility for these new interpolyesters, for instance, gaskets can be prepared for employment in equipment operating at higher temperatures, fibers can be made which withstand higher ironing temperatures when fabrics are prepared from yarnsincorporating these fibers, etc.

One embodiment of this invention relates to a process for preparing an interpolyester. comprising. (A) condensing about 10 mole proportions of a sulfonyl dibenzoic compound having the forrnula:

wherein R1 and R4 each represent a substituent selected from the group consisting of a ,B-hydroxya lkyl radical containing from 2 to 4 carbon atoms, an omega-hydroxyalkyl radical containing from 3 to 12 carbon atoms and an alkyl radical containing from 1 to 6 carbon atoms, plus from about 1 to about 30mole proportions of a branchedchain aliphatic acid diester selected from those having the followingformula:

wherein R10 represents a divalent radical selected from the group consisting of an ethylidene radical and a branched-chain alkylene radicalcontaining from 3 to 12 carbon atoms, and R andRaeach represents a substituent selected from the group consisting of an omega-hydroxyalkyl radical containing from 2 to 12 carbon atoms and an alkyl radical containing from 1 to 6 carbon atoms,v '(B) with a dioXy compound selected from the group consisting of those compounds having the following formulas:

wherein p represents a positive integer of from 2 to 12, R5 and Rs each represents a substituent selected from the group consisting of a hydrogen atom and an acyl radical containing from 2 to 4 carbon atoms, R7 represents an alkylene radical containing from 2 to 4 carbon atoms and q represents a positive integer of from 1 to inclusive, the dioxy compound being employed in such a proportion that there is at least an equivalent amount of oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the diesters and the dioxy compounds, (C) in the presence of a condensing agent selected from the group consisting of the alkali metals, the alkaline earth metals, the oxides of these two groups of metals, the alkoxides containing from 1 to 6 carbon atoms of these two groups of metals, the carbonates and borates of these two groups of metals, lead oxide, and compounds having the following formulas:

wherein M represents an alkali metal, M' represents an alkaline earth metal selected from the group consisting of magnesium, calcium and strontium, R represents an alkyl group containing from 1 to 6 carbon atoms, R, R" and R each represents a member of the group consisting of R and an aryl group of the benzene series containing from 6 to 9 carbon atoms and Hal represents a halogen atom, (D) at an elevated temperature, (E) the condensation being conducted in an inert atmosphere, and (F) the latter part of the condensation being conducted at a very low pressure of the inert atmosphere.

Advantageously, the dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the diesters and the dioxy compounds. Advantageously, the low pressure defined under (F) is less than about mm. of Hg pressure. Advantageously, the elevated temperature employed during the earlier part of the condensation is from about 150 to about 220 C. Advantageously, the dioxy compound is a glycol having the formula:

HO- (CH2 p-OH wherein p is defined under (B) above.

The dioxy compounds defined above may not actually contain any free hydroxy radicals since they may be in esterified form as indicated by the formulas given. How ever, these hydroxy or substituted hydroxy radicals are referred to generically as oxy radicals or substituents. The dioxy compounds which can be employed in accordance with this invention are most advantageously dihydroxy compounds; such compounds will hereinafter be referred to as dihydroxy compounds although it is to be understood that dioxy compounds of the type described above are intended to be covered by this term. Each diester is considered as containing two carbalkoxy radicals as that term is employed in the definition of the process as described above since R1 and R4 may be alkyl radicals, omega hydroxyalkyl radicals or fl-hydroxyalkyl radicals and Re and R9 may be alkyl radicals or omega hydroxyalkyl radicals. Even when the process is preceded by the preliminary step described below employing free acids, the term carbalkoxy radicals in the description of the process is intended to encompass such free carboxy radicals.

Furthermore, this invention covers a process as defined above wherein either or both of the sulfonyl dibenzoic acid diester and the aliphatic acid diester is/ are formed by a preliminary step comprising condensing free p,p sulfonyl dibenzoic and/or free aliphatic acid with a dihydroxy compound which is defined under (B) and is employed in the proportions set forth under (B), at an elevated temperature, after which preliminary step the condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F). Advantageously the elevated temperature employed during the preliminary step is substantially that at which reflux conditions subsist; however, higher and lower temperatures can also be employed. Advantageously, as indicated above the dihydroxy compound is employed in such a proportion that there are from about 1.2 to about 3 hydroxy substituents in proportion to the carboxy and carbalkoxy substituents in the overall combination of the diacids, diesters, and dihydroxy compounds.

As indicated above, the interpolyesters described herein have relatively wide softening ranges and good flow properties. In this respect, they differ from most types of high-melting linear polyesters, such as polyethylene terephthalate, which possesses sharp melting points. Thus, these modified polyesters of sulfonyl dibenzoic acid soften over a sufficiently wide temperature range that they can be advantageously employed in the production of shaped objects by injection molding and extrusion methods.

The alkylene glycols which can be employed to form highly polymeric linear polyesters are straight-chain alkane diols, viz. polymethylene glycols, wherein the hydroxy radicals are positioned at the two ends of the alkylene chain. Examples of such glycols include ethylene glycol, 1,3-propylene glycol, l .4butylene glycol, 1,6- hexylene glycol, 1,10-decamethylene glycol, 1,12-dodecamethylene glycol, etc. As indicated above, mono or diesters of these glycols can also be employed. Thus, the acetates, propionates and butyrates are examples of such esters. The defined ether glycols can be employed either in lieu of the polymethylene glycols or in conjunction therewith as modifiers. Mixtures of alkylene glycols or ether glycols can also be employed. Examples of ether glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, bis (4-hydroxybutyl) ether, bis (3-hydroxypropyl) ether, etc. When mixtures of alkylene glycols and ether glycols are employed, it is generally preferable to employ a major proportion of the alkylene glycol in order to obtain higher melting linear polyesters. The high melting characteristic also is dependent upon the amount of branched-chain aliphatic dibasic acid present in the interpolyester, the chain length of this aliphatic acid and the chain length of the glycol employed. Higher proportions of the aliphatic acid lower the melting and softening temperatures of the interpolyesters. This effect is also produced when a longer chain-length aliphatic acid is employed in the same proportions as a shorter chain length acid. Moreover, this effect is also dependent upon the manner in which the branching in the aliphatic chain takes place. The same effect is created by employing a longer chain (higher carbon content) alkylene glycol. For example, when a 10-l2 carbon atom glycol is employed, the amount of aliphatic ether glycol used should preferably be not more than about 10-20 mole per cent; whereas, when a 2-4 carbon atom glycol is employed the amount of ether glycol can be as high as about 50 mole per cent of the total quantity of dihydroxy compounds employed. When no ether glycol is employed, it is preferred to employ polymethylene glycols containing from 4 to 8 carbon atoms; this is especially important when the aliphatic acid has a rather short chain length, the proportion thereof is relatively low and the polymethylene glycol also has a short chain length (e. g. ethylene and trimethylene glycol) under which conditions the mole ratio of the p,p sulfonyl dibenzoic ester to the aliphatic diester should be from 10:10 to 10:30 since the melting point of the interpolyester produced might otherwise be above 300 C. whereby decomposition would take place whenever the polyester was melted or softened.

Valuable fibers having high melting temperatures can be prepared by incorporating very little, preferably none, of an aliphatic ether glycol and less than 15 mole per cent of the aliphatic dibasic acid (of the type described above) grid-$1992 into an interpolyester containing about 85-790 mole per cent of the p,p'-su1fonyl dibenzoic constituent. It is. particularly adgantageous to employ a polymethylene glycol containing from to 8 carbon" atoms and an aliphatic branched-chain acid diester containing from 4 to carbon atoms in the acid portion of the diester when it is desired to obtain fibers having a pronounced degree of elastic extensibility. For general molding and extrusion purposes, glycols containing from 2 to 6 or 8 carbon atoms and the 4 to 10 carbon atom acid diesters are usually to be preferred. However, on the other hand, valuable interpolyesters can be prepared employing aliphatic ether glycols without any alkylene glycol although the product obtained will not be suitable for forming useful fibers.

The catalytic condensing agents which can be employed have been described above. From about 0.005% to about 0.2% of such catalysts based on the weight of the reactants being condensed can be employed. Higher or lower percentages can also be employed. Generally, from about 0.01%to about 0.06% of the catalytic condensing agent can be advantageously employed based on the weight of the various diesters being condensed.

The temperature at which polyesterification can be conducted is dependent upon the specific reactants involved in any given reaction. In general, the reaction mixture can be heated at from about 150 to about 220 C. for from approximately two to three hours in an inert atmosphere (e. g. nitrogen or hydrogen); the mixture can then be heated at from about 225240 to about 280-3l0 C. in the same atmosphere for approximately 1 to 2 hours. Finally, the pressure can be greatly reduced to form a vacuum (less than about mm. of Hg pressure but preferably on the order of less than 5 mm. of Hg pressure) while the temperature is maintained in the same range (225 310 C.); these conditions are advan-- tageously maintained for approximately 4 to 6 additional hours. This final phase is advantageously carried out with good agitation under the high vacuum in order to facilitate the escape of volatile products from the highly viscous melt. The conditions can be: varied considerably depending upon the degree of polyesterification desired, the ultimate properties sought, the stability of the polyester being produced, and the use for which the product is intended. Thus, the extent of the substitution of the sulfonyl dibenzoic diesters with the esters of additional modifying acid necessitates variations in these conditions of temperature, pressure and time periods required. The employment of the novel catalytic condensing agents listed hereinabove results in better products being prepared in much less time than is possible when the catalysts of the prior art are employed.

It has been found that the type of catalyst used has an important bearing upon the properties of the final product. Although most of the catalysts cited in the prior art may be used, it has been found that certain novel catalysts give superior results. The aluminum and titanium alkoxide complexes described in copending applications filed on even date herewith are especially valuable for the preparation of the polyesters described here. Moreover, novel tin catalysts have also been foundto be especially effective. See Caldwell Serial No. 313,072, Serial No. 313,078, oudwu and Reynolds Serial No. 313,077, Wellrnan and Caldwell Serial No. 313,074, Serial No. 313,075 and Serial N013 13,076, and Wellman Serial No. 313,073 for a description of especially advantageous catalytic condensing agents.

The reaction can be carried out in the presence or absence of a solvent. Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixed tolyl sulfones, chlorinated naphthalene, chlorinated diphenyl, dimethyl sulfolane, etc, be used as the reaction medium.

It is important to exclude oxygen and moisture at all sa a l 'thesna asatia rsa ti Inert atmospheres 'uhis fs'a h ad ant s ws wv s include nitrogen,

hyd ogen. h lium q- Substan a ly a h d ous rsa t nt 2m al b dva ous y p oyed a u h s s n essential, especially if any water is removed in the earlier stages of the condensation.

As indicated above, the acidic constituents of the inter polyesters are employed in the form of their diesters. The

omega-hydroxyalkyl diesters can be prepared as described above by heating a polymethylene glycol (or an aliphatic ether glycol) with the free acid, preferably employing an excess of the glycol. The beta-hydroxyalkyl diesters can be prepared as described in my parent application employing an alkylene oxide. The acid chlorides can be employed in some cases although the conditions involved are generally substantially dilferent.

Examples of the various diesters which can be employed in accordance with the process of this invention include the ethyl, propyl, n-butyl, sec-butyl, isopropyl, sec-amyl, n-hexyl, IO-hydroxydecyl, 5- hydroxyamyl, 12-hydroxydodecyl, 2-hydroxyethyl, etc. diesters of either p,p'-sulfonyl dibenzoic acid or any of the aliphatic branchedchain dibasic acids of the type described above. When the novel catalytic condensing agents described hereinabove and in copending applications referred to herein are employed, the simple alkyl esters of these various dibasic acids can be advantageously employed, whereas if the catalysts known to the prior art are employed, the condensation will not proceed as rapidly or as effectively although satisfactory results can be obtained.

The aliphatic branched-chain dibasic acids encompassed within the scope of this invention contain from 1 to 8 carbon atoms in a straight chain between the carboxyl groups and have one or more alkyl substituents attached to this chain. The attached alkyl substituents can contain from 1 to 4 or more carbon atoms and can also be branched. The alkyl group is advantageously a methyl,

ethyl, propyl or butyl radical although isopropyl, sec-butyl and other alkyl radicals can also be present. Two of the substituent alkyl radicals can be attached to the same carbon atom when they are methyl or ethyl groups. Examples of suitable acids include: dimethyl malonic, methyl succinic, a,a-dimethyl succinic, u,fi-dimethyl succinic, ethyl succinic, butyl succinic, e-methyl glutaric, a,fl-dimethyl glutaric, e-methyl adipic, fi-propyl adipi'c, -ethyl pimelic, and ,B-methyl sebacic, etc. In general, the position of the alkyl group has little or no influence on the utility of the acid, although it may have some effect on'the properties of the polyester, e. g. the melting point.

The advantageous ratio of p,p'-sulfonyldibenzoic diester to the modifying aliphatic dibasic acid diester will depend upon the type of product desired. As the mole percent of the modifying acid in the polyester is increased, the melting point of the product is lowered. When short chain glycols such as ethylene glycol and tetramethylene glycol are used, it is usually preferable to employ from 1 to 3 moles of the modifying acid diester for each mole of p,p'-sulfonyldibenzoic diester in order to keep the melting point of the product below its decomposition temperature. When higher glycols such as pentamethylene, hexamethylene, and octamethylene glycol are used, from about 1 to about 7 or 8 moles of the aliphatic branched-chain dibasic acid diester can be employed for each ten moles of p,p'-sulfonyl dibenzoic acid.

As indicated hereinabove, some of the isomers of p,psulfonyl dibenzoic acid can be employed under some circumstances with resultant lowering of the melting or softening temperatures but with a probable increase in the softening range of temperatures. The same effect is produced when homologs of p,p-sulfonyl dibenzoic acid are incorporated into the materials being condensed to prepare these interpolyesters. If homologs are employed theyare most advantageously those of p,p'-sulfonyl dibenzoic acid, e. g. m,m'-dimethyl-p,p'-sulfonyl dibenzoic acid, o-ethyl-p,p'-sulfonyl dibenzoic acid, m-methyl-o-propyl-p,p-sulfonyl dibenzoic acid, etc.

Small proportions of various diesters of such isomers and homologs can be employed in substitution for a corresponding quantity of the diester of p,p-sulfonyl dibenzoic acid when the interpolyester product is not intended to be used in the preparation of fibers.

The products of this invention are linear inter-polyesters which possess favorable flow characteristics over a temperature differential or range of about to 20 C., a low modulus of elasticity and which contain in the interpolyester configuration a ratio of about of one of the following repeating units:

to each 1 to about 30 of one of the following repeating units:

wherein R10 and p are defined above.

When the ratio of the repeating units is, respectively, from about 10:1 to about 10:2 these interpolyesters are capable of being spun into fibers which can be drawn to from about 3 to 6 times their originally spun length thereby developing strong, elastic properties distinguished by a high degree of reversible extensibility.

The above described interpolyesters can also have either one or both of the two types of repeating units depicted above replaced by entirely or in part, respectively, one of the following repeating units:

wherein R10 and q are defined above.

In the examples given below, the hot bar sticking temperature is referred to in several instances. The hot bar sticking test can be briefly described as follows: A polyester fiber is placed on the flat surface of a heated bar and a weight of 100 grams is applied to the fiber along a distance of inch of the fiber length. The contact surface of this weight has a coating of polytetrafluoroethylene which acts as a thermal insulator. The fiber is allowed to remain in contact with the bar under this weight for one minute. The minimum temperature at which the fiber adheres to the hot bar under these conditions is the sticking temperature as that term is employed in the examples given herein.

This invention can be further illustrated by the following examples; in addition to these examples it is apparent that other variations and modifications thereof can be adapted to obtain similar results:

Example 1.tz,ot-Dimethyl glzltaric acid and letmmethylene glycol Four hundred and twenty grams (1.0 mol) of p,p-sulfonyldibenzoic acid dibutyl ester, 190 grams (1.0 mol) of o e-dimethyl glutaric acid dimethyl ester, and 360 g. (4.0 mol) tetramethylene glycol were placed in a reaction vessel equipped with a stirrer, a short distillation column, and an inlet for purified hydrogen. Ten cc. of butyl alcohol containing 0.25 g. sodium titanium butoxide was added as a catalyst and the mixture was heated at 200 210 C. with stirring. After one or two hours, the evolution of butyl and methyl alcohols had practically ceased, showing that the ester interchange was complete. The temperature was then raised to 260-270 and held for 30 minutes. A vacuum of 0.5 to 1.0 mm. of Hg pressure was then applied while the heating and stirring were continued for 2 /2 to 3 hours. A colorless product was obtained having an inherent viscosity of 0.7 to 0.8 in 60% phenol-40% tetrachlorethane solution. This interpolyester begins to flow under pressure at about 180 C. and gradually becomes softer as the temperature is raised. It does not have a sharp melting point. Because of its relatively wide softening range, the interpolyester is espe- Four hundred and twenty grams (1.0 mol) p,p-sulfonyldibenzoic acid dibutyl ester, 300 g. (1.6 mol) ,0:- dimethyl glutaric acid dimethyl ester, and 360 g. ethylene glycol were placed in a reaction vessel equipped with a stirrer, a short distillation column, and an inlet for purified nitrogen. A solution of 0.3 g. sodium titanium butoxide in 10 cc. butyl alcohol was added as a catalyst. The mixture was stirred at 180190 C. in a stream of nitrogen. A mixture of butyl and methyl alcohols dis tilled off. The esterinterchange was essentially complete in 2 hours. The temperature was then raised to 270-275 C. and held for 30 minutes. A vacuum of 1.0 to 2.0 mm. of Hg pressure was then applied, while stirring was continued for l to 1 /2 hours. The product obtained has an inherent viscosity of 0.6 to 0.70 in 60% phenol-40% tetrachlorethane. The interpolyester tends to be more hard and rigid than the one described in Example 1 Where tetramethylene glycol was used. This product shows good fiow characteristics when molded by injection methods. Films can be cast from tetrachlorethane solutions. They can be used as photographic film base materials.

Example 3.Dimetlzyl malonic acid and pentamethylene glycol Three hundred and seventy-two grams (1.0 mol) of p,p-sulfonyldibenzoic acid diethyl ester, 95 g. (0.5 mol) dimethylmalonic acid diethyl ester, and 300 g. pentamethylene glycol were placed in a reaction vessel as described in Example 1. A solution of 0.2 g. of sodium aluminum ethoxide in ethyl alcohol was added as a catalyst. The mixture was heated and stirred at 200210 C. in a stream of pure nitrogen for 2 hours to remove ethyl alcohol. The temperature was then raised to 250 C. and held for 30 minutes. A vacuum of 2.0 to 3.0 mm. of Hg pressure was then applied for 2 hours. The product obtained had a softening point of about 200 C. After it has been oriented and heat treated, it sticks to the hot bar at 180190 C. This interpolyester can be molded and extruded to give products that show good impact properties. It is useful as a photographic film base and as an electrical insulation.

Example 4.l3-Methyl adipic acid and hexamethylene glycol A polyester product having the composition: 0.75 mol p,p-sulfonyldibenzoic acid+0.25 mol fl-methyl adipic acid+l.0 mol hexarnethylene glycol was prepared by Example 5.- y-Ethyl glutaric acid and pentamethylene glycol A polyester having the composition: 0.80 mol p,p'-sul fonyldibenzoic acid+0.20 mol 'y-ethyl glutaric acid+1.0 mole pentamethylene glycol was made by reacting these gram mole quantities of the two acid ethyl diesters with 2 gram moles of pentamethylene glycol in exactly the same manner as described in Example 1. The product obtained wagons was an inter-polyester similar in most respects to those described by Example 1 and by Example the properties were more or less intermediate between those of these examples. The product obtained can be fabricated by extrusion and by injection molding processes.

Example 6.a,fi-Dimethyl succinic acid and octamethylene glycol A polyester having the composition: 0.60 mole p,p-sulfonyldibenzoic acid-l-OAO mole a e-dimethyl succinic acid+1.0 mole voctamethylene glycol was prepared by reacting these gram mole quantities of the two acid ethyl diesters with 2 moles of octamethylene glycol in exactly the same manner as described in Example 1. The product obtained was an interpolyester similar to that described in Examples 1 and 5 except for a lower softening and hot bar sticking temperature; however, this interpolyester is useful in manufacturing shaped objects by extrusion methods and can also be employed for other purposes.

Example 7.-Dimethyl malonic acid, ethylene glycol and diethylene glycol 1.75 gram moles of p,p-sulfonyl dibenzoic acid diethyl ester (650 grams 0.25 gram mole of dimethylmalonic acid diethyl ester (48 grams 1.5 gram moles of ethylene glycol and 1.5 gram moles of diethylene glycol were placed in a reactionvessel as described in Example 1. A solution of 1.0 gram of sodium aluminum ethoxide in ethyl alcohol was added as the catalyst. The mixture was heated and stirred at 190-200 C. in a stream of pure'nitrogen for 3 hours to remove ethyl alcohol. The temperature was then raised to 245 C. and held for 50 minutes. The pressure was then reduced to 0.5-1.0 mm. of Hg pressure for 6 hours. The product obtained had a softening point of about 180 C. This interpolyester can be molded and extruded to give products having good reversible extensibility.

. rates inherent in the change of the catalyst.

In the description herein-above and in the claims the term branched-chain alkylene radical clearly is intended to cover divalent alkylene radicals which include the following examples: 1,3-butylene and 2,5-hexylene, which radicals have the formulas:

C HIT-C Ea -([3 H CH3 and 6 CH C H3 7H2CH-CH2-(EH What I claim is: 1. A process for preparing a linear polyester comprising (A) condensing about 10 mole proportions of a p,p-sulfonyl dibenzoic diester having the formula:

wherein R1 and R4 each represents a substituent selected from the group consisting of a fi-hydroxyalkyl radical containing from 2 to 4 carbon atoms, an omega-hydroxyalkyl radical containing from 3 to 12 carbon atoms and an alkyl radical containing from 1 to 6 carbon atoms, plus from about 1 to about 30 mole proportions of an aliphatic diester selected from those having the following formula:

RaO-OCR1o-CO-OR9 wherein Rio represents a divalent radical selected from the group consisting of an ethylidene radical and a branched-chain alkylene radical containing from 3 to 12 carbon atoms, and Rs and R9 each represents a substituent selected from the group consisting of an omega-hydroxyalkyl radical containing from 2 to 12 carbon atoms and an alkyl radical containing from 1 to 6 carbon atoms, (B) with a dioxy compound selected from the group consisting. of those compounds having the following formulas:

wherein p represents a positive integer of from 2 to 12,v R5 and Rs each represents a substituent selected from thegroup consisting of a hydrogen atom and an acyl radical containing from 2 to 4 carbon atoms, R7 represents an alkylene radical containing from 2 to 4 carbon atoms and q represents a positive integer of from 1 to 10 inclusive, the dioxy compound being employed in such a proportion, that there is at least an equivalent amount of oxy substitucuts in proportion to the carbalkoxy substituents in the: overall combination of the diesters and the dioxy compound, (C) in the presence of a condensing agent selected from the group consisting of the alkali metals, the alkaline earth metals, the oxides of these two groups of metals, the alkoxides containing from 1 to 6 carbon atoms of these two groups of metals, the carbonates and borates of these two groups of metals and lead oxide, (D) at an elevated temperature, (E) the condensation being conducted in an inert atmosphere, and (F) the latter part of the condensation being conducted at a very low pressure of the inert atmosphere, said process encompassing the condensation of only those compounds referred to in (A) and (B) hereinabove.

2. A process as defined in claim 1 wherein the elevated temperature is increased gradually during the course of the condensation up to a temperature of from about 225 to about 310 C.

3. A process as defined in claim 2 wherein the condensing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the diesters employed.

4. A process as defined in claim 3 wherein the dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the diesters and the dioxy compounds.

5. A process as defined in claim 4 wherein the elevated temperature employed during the earlier part of the condensation is from about to about 220 C. and the low pressure defined under (F) is less than about 15 mm. of Hg pressure.

6. A process as defined in claim 5 wherein all materials employed in the process are substantially anhydrous.

7. A process as defined in claim 6 wherein the dioxy compound has the formula:

wherein p is defined under (B).

8. A process as defined in claim 7 wherein the aliphatic diester is dimethyl a,a-dimethylglutarate and the dihydroxy compound is tetramethylene glycol.

9. A process as defined in claim 7 wherein the aliphatic diester is dimethyl a,a-dimethylglutarate and the dihydroxy compound is ethylene glycol.

10. A process as defined in claim 7 wherein the aliphatic diester is diethyl dimethylmalonate and the dihydroxy compound is pentamethylene glycol.

11. A process as defined in claim 7 wherein the aliphatic diester is diethyl 'y-ethylglutarate and the dihydroxy compound is pentamethylene glycol.

12. A process as defined in claim 6 wherein the aliphatic diester is dimethyl dimethylmalonate and the dihydroxy 11 compound is made up of an equimolecular mixture of ethylene glycol and diethylene glycol.

13. A process as defined in claim 1 wherein the sulfonyl dibenzoic diester is formed by a preliminary step comprising condensing p,p-sulfony1 dibenzoic acid with a dioxy compound which is defined under (B) and is em ployed in such a proportion that there is at least an equivalent amount of oxy substitutents in proportion to the carboxy substitutents in the over-all combination of the dibenzoic acid and the dioxy compound, at an elevated temperature, after which preliminary step the condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F).

14. A process as defined in claim 13 wherein the preliminary elevated temperature is substantially that at which reflux conditions subsist, the subsequent condensation being conducted at a temperature which is gradually increased during the course of the condensation up to about 2803 C. and the dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 oxy substituents in proportion to the carboxy and carbalkoxy substituents in the overall combination of the diacids, diesters and dioxy compounds.

15. A process as defined in claim 1 wherein the aliphatic diester is formed by a preliminary step comprising condensing an aliphatic acid selected from the group having the following formula:

HOOCR10COOH wherein R10 represents a divalent radical selected from the group consisting of an ethylidene radical and a branchedchain alkylene radical containing from 3 to 12 carbon atoms, with a dioxy compound which is defined under (B) and is employed in such a proportion that there is at least an equivalent amount of oxy substitutents in proportion to the carboxy substitutents in the over-all combination of the dibenzoic acid and the dioxy compound, at an elevated temperature, after which preliminary step the condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F).

16. A process as defined in claim 15 wherein the preliminary elevated temperature is substantially that at which reflux conditions subsist, the subsequent condensation being conducted at a temperature which is gradually increased during the course of the condensation up to about 280-310 C., and the dioxy compound is employed in such a proportion that there are from about 1.2 to

about 3 oxy substituents in proportion to the carboxy and carbalkoxy substituents in the overall combination of the diacids, diesters and dioxy compounds.

17. A process as defined in claim 16 wherein the condensing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the diesters being condensed, the elevated temperature employed during the earlier part of the condensation to form the interpolyester is from about C. to about 220 C. and the low pressure defined under (F) is less than about 15 mm. of Hg pressure.

18. A linear interpolyester having a softening temperature differential of from about 5 to 20 C. consisting of a ratio of about 10 of one of the following repeating units:

to each 1 to about 30 of one of the following repeating units:

wherein R10 represents a divalent radical selected from the group consisting of an ethylidene radical and a branched-chain alkylene radical containing from 3 to 12 carbon atoms, and 2 represents a positive integer of from 2 to 12, which interpolyester has a low modulus of elasticity and is capable of being readily formed into shaped objects within its softening range and wherein the (CH2)17' units in the molecular structure include a substantial proportion of such units wherein p is at least 4.

19. A linear interpolyester as defined in claim 18 wherein at least one of the repeating units depicted therein is replaced by the following repeating unit corresponding thereto:

wherein R10 represents a divalent radical selected from the group consisting of an ethylidine radical and a branched-chain alkylene radical containing from 3 to 12 carbon atoms, R7 represents an alkylene radical containing from 2 to 4 carbon atoms and q represents a positive integer of from 1 to 10.

20. A linear interpolyester as defined in claim 18 wherein p is 4 and R10 is a 1,1-dimethyl-1,3-propylene radical.

21. A linear interpolyester as defined in claim 18 wherein p is 2 and R10 is a 1,1-dimethyl-1,3-propylene radical.

22. A linear interpolyester as defined in claim 18 wherein p is 5 and R10 is a dimethyl-methylene radical.

23. A linear interpolyester as defined in claim 18 wherein p is 5 and R10 is a 1-ethyl-1,3 propylene radical.

References Cited in the file of this patent UNITED STATES PATENTS 2,437,046 Rothrock et al Mar. 2, 1948 2,465,319 Whinfield et al. Mar. 22, 1949 2,547,113 Drewitt et al. Apr. 3, 1951 2,623,033 Snyder Dec. 23, 1952 FOREIGN PATENTS 621,997 Great Britain Apr. 25, 1949 

1. A PROCESS FOR PREPARING A LINEAR POLYESTER COMPRISING (A) CONDENSING ABOUT 10 MOLE PROPORTIONS OF A P,P''-SULFONYL DIBENZOIC DIESTER HAVING THE FORMULA: 